1. Field of the Invention
The present invention relates to a waste heat recovery device which recovers waste heat of exhaust gas using a heat pipe.
2. Description of the Related Art
Conventionally, a heat pipe including an iron container having therein water is used. The heat pipe is suitably used for various applications because the iron container has a high strength and water has a high performance as a working fluid. However, when iron reacts with water, hydrogen gas is generated, and the hydrogen gas reduces a performance of the heat pipe for a short time.
As a technique for preventing a performance reduction of the heat pipe due to the hydrogen gas, for example, JP-U-50-49064 discloses a heat pipe in which at least a part of a container is made of palladium or a palladium-based alloy through which hydrogen gas permeates. In addition, U.S. Pat. No. 4,782,890 (corresponding to JP-A-6-66486) discloses a heat pipe in which a porous sintered body is arranged in a condensing part of the container. The porous sintered body is made of an oxidizer for oxidizing hydrogen gas into water. Further, U.S. Pat. No. 4,773,476 (corresponding to JP-A-61-76883) discloses a heat pipe which is made of aluminum, steel, or gray cast iron. The whole inner surface of the heat pipe is coated with a waterproof metal (e.g., copper, nickel, copper and nickel) for preventing a generation of hydrogen gas.
However, in the heat pipe disclosed in JP-U-50-49064, at least a part of the container is made of high-priced palladium or a palladium-based alloy, thereby a production cost of the heat pipe may increase compared with a heat pipe made of iron. Further, in the heat pipe disclosed in U.S. Pat. No. 4,782,890, the porous sintered body is arranged in the condensing part of the container, thereby the heat pipe has a complicated structure and a production cost of the heat pipe may increase. In addition, a part of the hydrogen gas generated in the heat pipe may be not oxidized. In the heat pipe disclosed in U.S. Pat. No. 4,773,476, the whole inner surface of the heat pipe is coated by the waterproof metal, thereby a production cost of the heat pipe also increases. Further, when a part of a coating is damaged by a thermal stress and the like, hydrogen gas may be generated, and a performance of the heating pipe may be reduced.
Furthermore, when the waste heat recovery device is used for a long term, noncondensable gas may be generated in the heat pipe, and may reduce a heat transport property of the heat pipe. Thus, the noncondensable gas is required to be removed from the heat pipe. For example, JP-A-55-82290 discloses a method for removing the noncondensable gas from the heat pipe. In the method, the heat pipe is heated so that the working fluid in the heat pipe evaporates and an inside pressure of the heat pipe becomes higher than an outside pressure (air pressure). The noncondensable gas is removed through a slit provided in a sealing part of the heat pipe. Then, the slit is sealed by brazing or welding.
However, the waste heat recovery device in JP-A-55-82290 requires a troublesome work to make the slit in the sealing part of the heat pipe and seal the slit after removing the noncondensable gas, at every time when the noncondensable gas is removed. Further, a part of the evaporated working fluid may be removed with the noncondensable gas. Thus, a performance of the waste heat recovery device may be reduced.
Further, JP-A-8-327188 discloses a noncondensable gas removal device. As shown in FIG. 15, the noncondensable gas removal device includes an adsorption type freezer 100, a first container 120, and a second container 140. The first container 120 is connected to the adsorption type freezer 100 through a first valve 110, and the second container 140 is connected to the first container 120 through a second valve 130. The first container 120 has a first adsorbent 150 which adsorbs water as a coolant at a low temperature and desorbs the water at a high temperature. The second container 140 has a second adsorbent 160 which adsorbs gas. The first valve 110 and the second valve 130 are electrically switched by a control device 170.
When the first valve 110 is opened, water vapor flows from a coolant passage of the adsorption type freezer 100 to the first container 120, and the water vapor is adsorbed by the first adsorbent 150. At the same time, the noncondensable gas in the water vapor is separated from the water vapor and remains in the first container 120. Next, the second valve 130 is opened. The noncondensable gas remaining in the first container 120 flows into the second container 140, and is adsorbed by the second adsorbent 160. Thus, the noncondensable gas is efficiently removed from the coolant passage in the adsorption type freezer 100.
When a waste heat recovery device has the noncondensable gas removal device disclosed in JP-A-8-327188, the waste heat recovery device becomes large, and a production cost may increase.